Wind-powered or wind-driven electricity generation devices, are a significant source of renewable electrical energy. Some are aligned horizontally, mounted on tall masts and resembling large propeller-equipped aircraft engines, and others are vertically aligned and equipped with two or more elongated vertical sail-like rotors. The present invention involves the latter group. While there have been many designs proposed or used for the wind-driven vertical rotors which drive the generators, very few have used Savonius drag-type rotors. It has been believed that lift-type rotors were more efficient for large scale devices, and Savonius rotors have been used primarily in small scale devices. See, e.g., Hayashi et al., JSME Int'l. J., Series B: 48 (1), 9-16 (2005).
In its most basic configuration, a Savonius rotor has an S-shaped cross-section and consists of a “blade pair” comprising two interconnected vertical blades with a small overlap between them. The blade pair is unitary and is mounted on a central vertical shaft. Commercial devices with Savonius rotors with unitary blade pair designs have been marketed by one manufacturer for small scale residential power generation. The same manufacturer has also commercialized similar devices in smaller sizes as chargers for batteries in such small installations as emergency beacons and small boat lighting. These are generally shown as requiring shaft support at both top and bottom of the rotor. In all of these designs each blade in the blade pair is also a unitary structure.
Savonius rotors may also have more than two interconnected blades; see, e.g., Grinspan et at., PROC. OF 28TH NAT'L. CONF. ON FLUID MECHANICS AND FLUID POWER, pp. 428-431 (Chandigarh, India: 2001). For the purposes of the invention herein, the number of blades is not critical, and two, three, four or more blades (two or three blades are the most practical) are all to be considered included in the invention. The term “blade pair” as used herein, therefore, shall be considered to encompass all such pluralities of blades, not just those containing only two blades. For brevity, however, the invention shall be discussed with respect to a two-blade “blade pair,” the preferred embodiment of the invention.
The inclusion of unitary blade pairs in any size other than the very smallest in such devices severely limits the devices use in many environments and for many uses because of problems in assembly, installation, maintenance and repair. Unitary blade pairs are large, heavy and unwieldy to handle and to install. Since the rotor is attached to the central vertical shaft over its entire length, this necessitates that for assembly, installation, repair and maintenance of the device the entire rotor must be handled as a single unit. For all except the smallest devices equipment such as a crane or some other type of large overhead lifting device must be employed. Efforts to avoid such problems have been made by providing intermediate structural supports, such as a series of horizontal plates, to the unitary vertical blades (Hayashi, supra.). While these may prevent or reduce the extent of damage to such a blade, repair or replacement of a damaged blade will still require the use of substantial removal and repair equipment and facilities. Such considerations belie the advertisement of vertical wind-driven electrical generation devices as suitable for residential use, since their installation, maintenance and other aspects of their use, even if nominally in a residential setting, necessarily requires the services of professional personnel using industrial equipment.
It would therefore be of substantial interest to have a commercially available wind-driven electrical generation device which would be a true “residential” installation level or small business installation level device, in that it could be readily handled, transported, assembled and maintained by a single individual such as a homeowner or small business owner or operator, without the need for assistance by heavy equipment. Such a device would be capable of producing a significant amount of electrical energy, either for direct use by the device owner such as for lighting or other power requirements, or for feedback into the electrical power grid to which the residence or business facility is connected, thus allowing the device owner to obtain electrical service credits against the fees otherwise charged for the electrical service provided from the grid. The device of the present invention provides these properties in a new and unique structure.